This question applies more to the more modern maps, rather than typical fantasy maps.

I'm working on an atlas for my world in a topographical style and I;'m having difficulty coming us with the heights for the different topographical layers.

To be honest, they're arbitrarily chosen at the moment, though when comparing the height level's I've chosen to real-world maps, they're way off - my topography gets steep far quicker. It seems as though most real-world maps don't use a linear progression to the heights, so heights get graduially steeper as you move up in topographical layers, with the first 3 layers (typically green) being a lot lower than the next 3.

Like I said, my heights are all arbitrary at the moment. Though I don't want to change the maps themselves, I'm fine with changing heights for each topographical level and spot heights into something more realistic.

Does anyone know of how (if) there is a system for determining these heights, or are they arbitrary depending on the map?

If it makes any difference my world is larger than earth and the highest peak is 31,000 ft (Everest is 29,029)